The present invention relates to a display picture element measuring method arranged such that, even though there is a positional shift between a display picture element and the corresponding light receiving picture element, the light amount of the display picture element can accurately be measured with neither display picture element nor light receiving picture element moved.
The present invention also relates to a display screen inspecting method and a display screen inspecting apparatus each arranged such that, even though there is a strain of a display screen or a positional shift between the display screen and an inspection screen when inspecting the display screen, there is established, with neither the display screen nor the inspection screen moved, a corresponding relationship between display picture elements and light receiving picture elements such that the light amount of the display picture elements is accurately measured.
Conventionally, a liquid crystal display screen is visually checked for quality. A considerably small display defect or irregularity can be judged even by such a visual inspection. However, the reliability on the evaluation depends on the experience or the like of an inspector. This assures no objectivity on the inspection result. Further, the visual inspection lowers the inspection speed.
To solve such problems, there is proposed an automatic inspecting method using a one-dimensional image sensor (line sensor) or a two-dimensional image sensor (See Japanese Unexamined Patent Publication Nos. 6-11679/1994 and 5-240802/1993).
The former Japanese Unexamined Patent Publication No. 6-11679 discloses the following invention. That is, a display picture element to be inspected is brought to a bright state while other picture elements in the vicinity of the display picture element to be inspected are brought to a dark state. A light receiving device is disposed for receiving the images of these picture elements to generate sensor picture elements, and the respective sensed light amounts of the sensor picture elements are then integrated. The resulting integrated value is considered as the light amount of the picture element to be inspected.
The latter Japanese Unexamined Patent Publication No. 5-240802 discloses the following invention. That is, on the assumption that display picture elements and light receiving picture elements are not always equal in number such that the display picture elements are not corresponding to the light receiving picture elements at 1:1, the positional relationship between a display screen to be inspected and a sensor camera is always set to a reference position, and the sensed light intensity information of a light receiving picture element is multiplied by a corresponding position correction coefficient extracted at the reference position, thereby to generate the light intensity information of the display picture element.
According to the invention of the former Japanese Unexamined Patent Publication No. 6-11679, almost all of the amount of light from the display picture element to be inspected can be detected to lower the amounts of lights from the adjacent picture elements. Accordingly, even though the relative position between the display picture element and the sensor picture element undergo a change more or less, the light amount of the picture element can be inspected. As a matter of fact, however, the sensor picture elements are not arranged leaving no spaces thereamong. Accordingly, there are present lights which do not enter sensor picture elements but are reflected or absorbed. In view of the foregoing, it cannot be said that the inspection precision of the light amount of each picture element is sufficiently accurate.
According to the invention of the latter Japanese Patent Laid-Open Publication No. 5-240802, it is required to precisely set the positional relationship between a display picture element and the sensor camera to the reference position at all times. This is because the setting error at the time when the positional relationship between a display picture element and the sensor camera is set to the reference position, will result in a detection level error. As a matter of fact, however, it is very difficult that, at the level of a picture element size, the display screen and the inspection screen are positionally set in a physically precise manner at the time of inspection. Further, if the display screen or the inspection screen has a strain, a display picture element cannot properly correspond to the light receiving picture element even though the display screen and the inspection screen are positionally set in a physically precise manner. This produces a subtle difference in spatial frequency between the arrangement of picture elements on the display screen and the arrangement of picture elements on the inspection screen. This results in moire fringes to exert a considerable influence upon the inspection.